1. Field of the Invention
The present invention relates to a flexible shaft coupling suitable for a propeller shaft used as a drive line component of a vehicle, and particularly to an axially flexible drive-shaft coupling designed to permit axial motion and thus to elastically absorb vibrations for axial directions.
2. Description of the Related Art
In recent years, there have been proposed and developed various shaft couplings capable of absorbing axial vibrations. Such shaft couplings have been disclosed in Japanese Utility-Model Provisional Publication Nos. 63-178632 (hereinafter is referred to as JP63-178632) and 60-189620 (hereinafter is referred to as JP60-189620). FIGS. 10 and 11 show a conventional shaft coupling disclosed in JP63-178632, in which the shaft coupling, called xe2x80x9ccentering bushingxe2x80x9d is used between the output shaft of the transmission and the propeller shaft. A plurality of bushes 2 are provided in a substantially annular main body 1 made of an elastic or elastomeric rubber material so that the bushes are circumferentially equidistant spaced to each other. The respective two adjacent bushes (2, 2) are connected to each other by means of a reinforcing wire 8 having a high rigidity (see FIG. 11). As best seen in FIG. 10, the first shaft (the transmission output shaft) 3 has a yoke 5 at its one axial end, whereas the second shaft (the propeller shaft) 4 has a yoke 6 at its one axial end. Yoke 5 has a plurality of branched arms (5a, 5a, 5a) circumferentially 120xc2x0-spaced with each other, while yoke 6 has a plurality of branched arms (6a, 6a, 6a) circumferentially 120xc2x0-spaced with each other. As can be seen in FIG. 11, the first group of branched arms (5a, 5a, 5a) alternate with the second group of branched arms (6a, 6a, 6a), sandwiching the annular main body 1 therebetween. These branched arms are bolted to the respective bushes 2 of shaft-coupling main body 1 by means of bolts 12. The axial end of first shaft 3 penetrates the central portion of shaft-coupling main body 1, and centered in the second shaft 4 through a substantially ring-shaped rubber bushing 7. Reinforcing wires 8 properly elastically permit relative displacement between first and second shafts 3 and 4. Reinforcing wires 8 also effectively rigidly transmit the rotational force (torque) byway of tension of the reinforcing wires. The shaft coupling shown in FIGS. 10 and 11, is complicated in structure, thus increasing the number of component parts and resulting in a large-sized coupling assembly. Instead of using the axially flexible shaft coupling shown in FIGS. 10 and 11, a simple, metal-plate, shaft coupling (as disclosed in JP60-189620) as shown in FIG. 12 is often used. As shown in FIG. 12, the metal-plate shaft coupling is comprised of a plurality of substantially annular metal plates 9 each having a plurality of bolt holes 10 formed therein and circumferentially equidistantly spaced to each other. Output-shaft coupled portions (corresponding to the first group of branched arms 5a) and input-shaft coupled portions (corresponding to the second group of branched arms 6a), alternating with each other in the circumferential direction, are bolted via the respective bolt holes 10 of each annular metal plate 9 with washers 11 to the substantially annular metal plates 9, sandwiching the annular metal plates between the first and second group of coupled portions. Each annular metal late 9 is a metal plate having a predetermined constant thickness that provides a comparatively high rigidity. Its radial width Axe2x80x2 is fixed to a certain value such that the metal plate 9 is generally annular in shape. A portion 9a extending between two adjacent bolt holes (10, 10) of metal plate 9 will be hereinafter referred to as a xe2x80x9ccoupling arm portionxe2x80x9d. Each coupling arm portion 9a is able to elastically deform or bend in the presence of input vibrations for each axial direction, so as to effectively dampen or absorb the axial vibrations. When torque (a rotational force acting in the direction of rotation) is applied to the metal-plate shaft coupling of FIG. 12, the coupling arm portion 9a serves to rigidly transmit torque therevia to the output side without any deformation, because of a high inertial mass in the rotational direction. In the shaft coupling as disclosed in JP60-189620, output and input shafts can be centered each other via the inner peripheral portion of each annular metal plate 9 having a high rigidity. This eliminates the necessity of a centering mechanism. On such annular metal-plate shaft couplings, there are two ways to enhance the axial vibration dampening effect. One way to effectively dampen axial vibrations, is to decrease the thickness of each annular metal plate 9 so as to reduce the rigidity of each coupling arm portion 9a for each axial direction. However, there are limitations to a reduction in the thickness of the annular metal plate. The other way is to lengthen the circumferential length of each coupling arm portion 9a. This undesirably increases the total size of the metal-plate shaft coupling. Generally, the metal-plate shaft coupling has worn portions around each bolt hole 10 owing to relative displacement of annular metal plate 9 to the bolts and relative displacement between two adjacent annular metal plates (9, 9) coaxially put side by side, during axial displacement of annular metal plates 9. Excessively thinner annular metal plate lowers the durability of the shaft coupling. Therefore, it is desirable to balance these contradictory requirements, that is to say, high durability, light weight (down-sized shaft coupling), and proper axial flexibility (enhanced axial vibration dampening effect).
In order to accomplish the aforementioned and other objects of the present invention, a flexible shaft coupling for a vehicle comprises a substantially annular plate having a plurality of mounting holes formed therein, a first group of coupled portions fixedly connected to a first shaft and circumferentially spaced with respect to each other, a second group of coupled portions fixedly connected to a second shaft and circumferentially spaced with respect to each other, the first and second groups of coupled portions being coupled with each other through the substantially annular plate placed therebetween, so that the first group of coupled portions circumferentially alternate with the second group of coupled portions, the substantially annular plate having coupling arm portions each extending between two adjacent mounting holes of the mounting holes to absorb vibrations for axial directions by elastic deformation of each of the coupling arm portions, and a radial width of each of the coupling arm portions being dimensioned to be narrower than a radial width of a peripheral region of each of the mounting holes.
According to another aspect of the invention, a flexible shaft coupling for a vehicle comprises a substantially annular plate serving as a torque-transmission member for rotational directions and having a plurality of mounting holes formed therein, a first group of coupled portions fixedly connected to a first shaft and circumferentially spaced with respect to each other, a second group of coupled portions fixedly connected to a second shaft and circumferentially spaced with respect to each other, the first and second groups of coupled portions being coupled with each other through the substantially annular plate placed therebetween, so that the first group of coupled portions circumferentially alternate with the second group of coupled portions, the substantially annular plate having coupling arm portions each extending between two adjacent mounting holes of the mounting holes to absorb vibrations for axial directions by elastic deformation of each of the coupling arm portions, and a thickness of each of the coupling arm portions being dimensioned to be thinner than a thickness of a peripheral region of each of the mounting holes.
According to a still further aspect of the invention, a flexible shaft coupling for a vehicle comprises a substantially annular plate serving as a torque-transmission member for rotational directions and having a plurality of mounting holes formed therein, a first group of coupled portions fixedly connected to an output shaft and circumferentially spaced with respect to each other, a second group of coupled portions fixedly connected to an input shaft and circumferentially spaced with respect to each other, the first and second groups of coupled portions being coupled with each other through the substantially annular plate placed therebetween by way of fastening means, so that the first group of coupled portions circumferentially alternate with the second group of coupled portions, the substantially annular plate having coupling arm portions each extending between two adjacent mounting holes of the mounting holes for the fastening means to absorb vibrations for axial directions by elastic deformation of each of the coupling arm portions, each of the coupling arm portions has a lightening hole formed therein, and each of the coupling arm portions is divided by the lightening hole into a first radial-outward arm portion placed outside of a hypothetical line segment between and including centers of the two adjacent mounting holes and a second radial-inward arm portion placed inside of the hypothetical line segment, and a sum of a radial width of the first radial-outward arm portion and a radial width of the second radial-inward arm portion being dimensioned to be narrower than a radial width of a peripheral region of each of the mounting holes.